Control of mastication and jaw function

Question 1

3 phases of swallowing

Answer 1

Oral phase - voluntary
Pharyngeal - involuntary
Oesophageal - involuntary

Question 2

Function of sensory receptors in muscles of mastication

Answer 2

Control muscle movement

Unevenly distributed

Question 3

Location of muscle spindles

Answer 3

Numerous in elevators and tongue muscles

Few in depressors

Question 4

Function of Golgi tendon bodies

Answer 4

Protect against overdevelopment of muscle tension
Unsure if they exist in elevator muscles
Performed by PDL receptors - limit the force applied in mastication

Question 5

Two types of muscle fibres

Answer 5

Extrafusal fibres - Contractile and makes up the bulk of the muscle
Intrafusal - only slightly contractile

Question 6

What makes up a muscle spindle

Answer 6

A bundle of intrafusal muscle fibres bound by a connective tissue sheath

Question 7

Function of a muscle spindle

Answer 7

Provides information on muscle length and the rate of change in muscle length
Aligned parallel with intrafusal fibres

Question 8

Nuclei of intrafusal fibres

Answer 8

Chainlike - nuclear chain type

Clumped - nuclear bag type

Question 9

Function of Golgi tendon organs

Answer 9

Provides information about muscle tension

Question 10

How do Golgi tendon organs work

Answer 10

In series with muscle fibres
The sensory dendrites of the gto afferent are interwoven with collagen fibrils
When the muscle contracts, collagen fibrils are pulled tights and this activates the Golgi tendon organ afferent

Question 11

What are pacinian corpuscles

Answer 11

Large oval organs made up of concentric lamellae of connective tissue
Widely distributed in various tissues
Used for perception of movement and firm pressure

Question 12

What is in the centre of each corpuscle

Answer 12

Core containing the termination of a nerve fibre

Question 13

What are nociceptors

Answer 13

Sensory receptors stimulated by injury or pain

Transmit information to the CNS via afferent nerve fibres

Question 14

Phases of the chewing cycle (masticatory stroke)

Answer 14

Jaw opening phase
Rapid jaw closing phase
Slow jaw closing phase (intercuspal) aka the power stroke

The jaw opening phase is longer than the jaw closing phase

Question 15

3 reflexes in the chewing cycle

Answer 15

The jaw jerk reflex
The jaw opening reflex
The unloading reflex

Question 16

What happens in the jaw jerk reflex

Answer 16

Simple reflex
Fibres from the mesencephalic nucleus synapse directly with the trigeminal motor nucleus which lifts the jaw
Can be evoked by tapping the chin
MONOSYNAPTIC REFELX

Question 17

What happens in the jaw opening reflex

Answer 17

Occurs as a result of mechanical or electrical stimulation of the lips, oral mucosa or teeth
Usually occurs when the teeth come into contact with a hard object in the mouth
Characterised by a brief period of inhibition of activity in the motor neurone of the jaw closing muscle
POLYSYNAPTIC REFLEX

Question 18

What happens in the unloading reflex

Answer 18

Occurs when food or other material between the jaws suddenly breaks or collapses and which helps stop the jaws forcefully coming together
Protects the teeth against occlusal loads
Characterised by decrease in masseteric activity and simultaneous increase in digastric activity
POLYSYNAPTIC REFLEX